Add token invariant to DiagnosticReporter

pkg/compiler/lib/src/resolution/constructors.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.resolution.constructors;
 
 import '../common.dart';
 import '../common/resolution.dart' show
     Feature;
 import '../compiler.dart' show
@@ skipping 48 matching lines @@
 
   DiagnosticReporter get reporter => visitor.reporter;
 
   bool isFieldInitializer(SendSet node) {
     if (node.selector.asIdentifier() == null) return false;
     if (node.receiver == null) return true;
     if (node.receiver.asIdentifier() == null) return false;
     return node.receiver.asIdentifier().isThis();
   }
 
-  reportDuplicateInitializerError(Element field, Node init, Node existing) {
+  reportDuplicateInitializerError(Element field,
+                                  Node init,
+                                  Spannable existing) {
     reporter.reportError(
         reporter.createMessage(
             init,
             MessageKind.DUPLICATE_INITIALIZER,
             {'fieldName': field.name}),
         <DiagnosticMessage>[
             reporter.createMessage(
                 existing,
                 MessageKind.ALREADY_INITIALIZED,
                 {'fieldName': field.name}),
         ]);
     isValidAsConstant = false;
   }
 
   void checkForDuplicateInitializers(FieldElementX field, Node init) {
     // [field] can be null if it could not be resolved.
     if (field == null) return;
     if (initialized.containsKey(field)) {
       reportDuplicateInitializerError(field, init, initialized[field]);
     } else if (field.isFinal) {
       field.parseNode(visitor.resolution.parsing);
       Expression initializer = field.initializer;
       if (initializer != null) {
-        reportDuplicateInitializerError(field, init, initializer);
+        reportDuplicateInitializerError(field, init,
+            reporter.withCurrentElement(field,
+                () => reporter.spanFromSpannable(initializer)));
       }
     }
     initialized[field] = init;
   }
 
   void resolveFieldInitializer(SendSet init) {
     // init is of the form [this.]field = value.
     final Node selector = init.selector;
     final String name = selector.asIdentifier().source;
     // Lookup target field.
@@ skipping 763 matching lines @@
     // constructors.
     return null;
   }
   // TODO(johnniwinther): Use [Name] for lookup.
   ConstructorElement constructor = cls.lookupConstructor(constructorName);
   if (constructor != null) {
     constructor = constructor.declaration;
   }
   return constructor;
 }